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Applications
Guard Bands
Guard bands enable test limits to be set to allow for the worst-case measurement error. The use
of guard bands in most instances improves the probability that there are no good instruments that
are found to be out of specification and no bad ones that are found to be in specification.
Calibrating instruments that use low-output thermocouples (TC's) or those that provide only a
small change in emf per degree (Seebeck effect) is most difficult since testing these instruments
requires a highly accurate and stable TC simulator.
Because the Model 1140A offers a new level of TC simulation accuracy, guard banding can be
reduced giving more assurance that the device-under-test is meeting its specification. For
example, if a data system is using Type S thermocouple material, and a test point is required at
1500°C, the nominal TC output is 15,581.67 µV and the Seebeck coefficient (emf change per
degree) is only 12.0369 µV. A lesser calibrator can provide only a calibration to 0.46°C whereas
the Model 1140A has an accuracy of 0.26°C. With accuracy demands increasing, 0.46°C may not
be tolerable.
Even for thermocouples in their normally used ranges, the Model 1140A's contribution to error
budget allows users virtually to ignore the calibrator's error margins.
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